The present invention relates to a reinforcing structure for a metal shell and a manufacturing method for a metal shell.
Generally, a drum includes a cylindrical shell and a pair of drum heads mounted to both side opening ends of the shell. When the drum is played, the drum head vibrates as a result of being beaten, and the vibration sound is amplified by the shell. In this manner, the drum shell not only functions as a fulcrum when the beaten drum head vibrates but also functions as a resonator which amplifies the vibration sound of the drum head. Based on this point, rigidity is required in the shell to prevent deformation due to tension of the drum head. However, when sound response and sustain, etc., are required, it is necessary to form the drum shell with a thin wall. In such a case, in order to form a thin-walled shell, reinforcement of only the opening ends to which drum heads are mounted has been performed.
In the case of a metal shell, as a method for forming reinforcing portions at opening ends of the shell, known is a method for, for example, as shown in FIG. 5, forming a cylinder from a rectangular metal plate and bending both opening ends of the cylinder to form reinforcing portions 51 that are V-shaped in cross-section. In addition, as a method for forming reinforcing portions at opening ends of a metal shell, for example, U.S. Pat. No. 1,832,227 discloses a method shown in FIGS. 6(A) to 6(D). According to this method, first, as shown in FIG. 6(A), two disks 61a and 61b are punched out of one metal plate 60. Next, as shown in FIG. 6(B), by pressing such as deep drawing or spinning, the disk 61a is shaped to form an upper shell 62a, and the disk 61b is shaped to form a lower shell 62b. Then, in order to form opening ends of a metal shell, a bottom central part P of each shell 62a, 62b is cut in a circle. Subsequently, as shown in FIG. 6(C), the opening end of each shell 62a, 62b is bent to form a reinforcing portion 63a, 63b that is triangular-shaped in cross-section, respectively. Lastly, both shells 62a and 62b are integrated by welding, whereby a metal shell 65 as shown in FIG. 6(D) is fabricated.
However, according to the method shown in FIG. 5, although a metal shell can be formed from a relatively small amount of material, since all parts of the metal shell are formed from one metal plate, the wall thickness cannot be differentiated between a trunk portion 50 and the reinforcing portions 51 of the metal shell. That is, since the reinforcing portions 51 are formed with the same wall thickness as that of the trunk portions 50, when the metal shell is formed with a thin wall, rigidity of the opening ends of the metal shell cannot be sufficiently secured. On the other hand, when a thick-walled metal plate is used to form a metal shell, opening ends of the metal shell cannot be skillfully bent, so that the reinforcing portions 51 cannot be formed in a desirable shape.
In addition, according to the method shown in FIGS. 6(A) to 6(D), since the reinforcing portions 63a and 63b that are triangular-shaped in cross-section are formed on both opening ends of a metal shell, the rigidity of the opening ends of the metal shell can be made higher than that by the method shown in FIG. 5. However, for this method, a die, a jig, and the like for deep drawing or spinning are necessary. In addition, this is not considered as a highly productive method, and as shown in FIG. 7, there is also a drawback that a large waste part (shaded part) is produced in the metal plate 60, which is a raw material. Furthermore, since a thick-walled portion is produced at a joint part between both shells 62a and 62b, there is also a problem that vibration of the metal shell is hindered, and the function as a resonator is impaired.